JP2020020633A - Thermal flow rate sensor - Google Patents

Abstract

To provide a thermal flow rate sensor having a high resistance to heat and a high responsive rate.SOLUTION: The thermal flow rate sensor includes: a substrate directly attached to a flow path in which a fluid flows; a first sensor in one of the front surface and the back surface of the substrate; a second sensor in one of the front surface and the second surface of the substrate, the second sensor being located below the first sensor; and a honeycomb structure having a plurality of holes extending in the thickness direction of the substrate divided by a separation wall in the substrate.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a thermal flow sensor.

  For example, a thermal flow sensor is used to measure a flow rate of a fluid supplied to a chamber in a semiconductor manufacturing process. Such a thermal type flow sensor has a metal thin tube that bypasses the upstream and downstream sides of a flow dividing element provided in a flow path, and a coil-shaped coil wound on the upstream and downstream sides of the thin tube, respectively. A first sensor and a second sensor are provided. The thermal type flow sensor is configured to measure the flow rate of the fluid flowing through the flow path based on the temperature measured by the first sensor and the second sensor, for example.

  By the way, in the semiconductor manufacturing process, it has been attempted in recent years to set the temperature of the fluid flowing through the flow path to a very high temperature near 300 ° C. When such a high-temperature fluid flows in the thin tube, the resin layer insulating between the thin tube and the first sensor and the second sensor wound around the thin tube may be melted, and a short circuit may occur. is there. As described above, it is difficult to measure the flow rate of a high-temperature fluid with the above-described thermal flow sensor from the viewpoint of heat resistance.

JP 2002-340647 A

  The present invention has been made in view of the above problems, and has as its object to provide a thermal flow sensor having high heat resistance and response speed.

  That is, the thermal type flow sensor according to the present invention includes a substrate mounted so that a surface faces a flow path through which a fluid flows, a first sensor formed on a front surface or a back surface of the substrate, and a front surface or a back surface of the substrate. A second sensor disposed downstream of the first sensor, and a honeycomb structure including a plurality of holes extending in the thickness direction of the substrate and defined by partition walls in the substrate. It is characterized by the following.

  In the present specification, the term “honeycomb structure” means that the shape of the cross section of the hole is not limited to a regular hexagon, but may be various shapes such as an octagon, a rectangle, a polygon such as a triangle, a circle, and an ellipse. It is a concept that includes things. Further, in the honeycomb structure, a plurality of the holes are provided side by side along a face plate direction of the substrate.

  In such a case, since the first sensor and the second sensor are formed on the surface of the substrate, the first sensor and the second sensor are formed by, for example, metal plating without using a resin having low heat resistance. Two sensors can be formed.

  Further, since the honeycomb structure is formed in the substrate, the heat capacity of the substrate can be reduced by the plurality of holes. For this reason, even if the difference in heat distribution between the case where the fluid is not flowing and the case where the fluid is flowing is slight, a temperature change in the substrate easily occurs immediately, and the first sensor and the second sensor use the same. The change can be detected with high sensitivity. Therefore, the response speed as a flow sensor can be improved.

  Furthermore, since the honeycomb structure is configured so that a plurality of holes extending in the thickness direction of the substrate are formed, the strength is maintained so that the substrate is not cracked even if the substrate is pressed in the thickness direction by the pressure of the fluid. be able to.

  From these facts, it is possible to detect even a small change in the flow rate of a high-temperature fluid in which it is difficult to measure the flow rate with the conventional thermal flow rate sensor.

  The substrate may be formed of quartz glass or ceramics in order to realize heat resistance and mechanical strength that do not cause damage even when exposed to a high-temperature fluid or subjected to pressure. . In addition, these materials have a large heat capacity as compared with other materials.However, due to the formation of the honeycomb structure, the heat capacity is reduced while the heat resistance and the mechanical strength are obtained. Accordingly, it is possible to increase the temperature change in the first sensor and the second sensor. Therefore, the response speed to the required flow rate can be secured.

  Even if a honeycomb structure is formed on the substrate, the surface side of the substrate can be made flat, and the first sensor and the second sensor can be easily formed by plating, vapor deposition, or the like while securing mechanical strength. Preferably, the first sensor and the second sensor are formed on the surface of the substrate, and the plurality of holes are opened on the back side of the substrate, and the front side of the substrate is closed. What is necessary is just a hole with a bottom.

  In order to increase the temperature difference between the first sensor and the second sensor so that the flow rate can be detected with higher sensitivity, the first sensor and the second sensor are formed on the surface of the substrate. What is necessary is just to be further provided with the heater arrange | positioned between.

  In order to increase the temperature of the substrate by heating the heater so that a larger temperature difference can be formed between the first sensor and the second sensor, the first sensor, the second sensor, The heater may be formed on the surface of the substrate, and the plurality of holes may be formed on the back side of the first sensor, the second sensor, and the heater.

  In order for the plurality of holes to be able to be filled in the finest plane along the face plate direction of the substrate, and to obtain mechanical strength while increasing the amount of reduction in heat capacity, the cross-sectional shape of the holes should be It may be a regular hexagon.

  In order that a sufficient temperature difference can be formed between the first sensor and the second sensor and, for example, a response speed required in a semiconductor manufacturing process can be realized, the first sensor and the second sensor are required. The distance between the sensor and the sensor in the direction along the surface may be 5 mm or less.

  The substrate may have a substantially disk shape having a diameter R, and the honeycomb structure may be formed in a region within a virtual circle having a radius of 0.35R or less from the center of the substrate.

  As described above, according to the thermal type flow sensor according to the present invention, since the first sensor and the second sensor are formed on the surface of the substrate that comes into contact with the fluid, for example, the resin insulator is formed by plating or vapor deposition. The heat resistance can be increased by not using a metal. Further, since the honeycomb structure is formed in the substrate, even if a material having heat resistance and a large heat capacity is used for the substrate, the plurality of holes are formed in the vicinity of the first sensor and the second sensor, The heat capacity of that portion can be reduced, and even a small change in the flow rate can be immediately detected as a temperature change. Therefore, the thermal type flow sensor according to the present invention can improve the response speed even when measuring the flow rate of a fluid near 300 ° C., for example.

FIG. 2 is a schematic diagram showing a state in which the thermal flow sensor according to the first embodiment of the present invention is attached to a flow path. FIG. 2 is a schematic cross-sectional view in the axial direction of the thermal flow sensor according to the first embodiment. FIG. 2 is a schematic diagram showing a front surface side of the thermal flow sensor according to the first embodiment. FIG. 2 is a schematic diagram showing the back side of the substrate of the thermal flow sensor according to the first embodiment. FIG. 7 is a schematic cross-sectional view in the axial direction of a thermal flow sensor according to a second embodiment of the present invention. The schematic diagram which shows the surface side of the thermal type flow sensor which concerns on 3rd Embodiment of this invention. The schematic diagram which shows the board | substrate of the thermal type flow sensor which concerns on 4th Embodiment of this invention. The schematic diagram which shows the surface side of the thermal type flow sensor which concerns on 5th Embodiment of this invention.

  A thermal flow sensor 100 according to a first embodiment of the present invention will be described with reference to FIGS.

  The thermal flow sensor 100 according to the first embodiment is used for measuring the flow rate of a high-temperature fluid supplied to a chamber or the like in a semiconductor manufacturing process, for example. For example, the fluid is a gas having a temperature of around 300 ° C. For measuring the flow rate of such a high-temperature gas at a response speed equivalent to that of a conventional flow sensor, for example, the thermal flow sensor 100 of the first embodiment is Used.

  As shown in FIG. 1, the thermal flow sensor 100 according to the first embodiment is attached to a narrow portion C1 of a flow channel C through which a high-temperature gas flows, where the flow channel diameter is small. Specifically, the thermal type flow sensor 100 includes a flange 1 attached to a pipe forming the flow path C, and a substrate 2 made of quartz attached to a tip of the flange 1. The surface 2H of the substrate 2 is provided so as to come into contact with the gas in the flow path C.

  FIGS. 2 and 3 are schematic views in which the thickness and the like are emphasized in order to make the details of each part of the substrate 2 and the members provided on the substrate 2 easy to understand. Therefore, the actual dimensional relationship is not always faithfully represented.

  As shown in FIGS. 2 and 3, a first sensor 3, a heater 5, and a second sensor 4 are sequentially provided on a surface 2 </ b> H of the substrate 2 formed in a substantially disk shape from an upstream side in a gas flow direction. ing. The surface 2H of the substrate 2 is a flat plate, and each member is formed by plating the surface 2H with metal by sputtering. Six through holes 21 are formed on the outer peripheral portion of the substrate 2 so as to form a regular hexagonal vertex, and the first sensor 3, the heater 5, and the second sensor 4 connect between the two through holes 21 respectively. Formed by metal plating.

  The first sensor 3 and the second sensor 4 are formed, for example, by sealing each through hole 21 with gold plating 31 and 41 and forming a platinum resistor formed of platinum plating 32 so as to have a zigzag portion between the gold plating. It is provided. The first sensor 3 and the second sensor 4 are arranged so as to be mirror-symmetric with respect to a center line of the surface 2H of the substrate 2 along the face plate direction. The first sensor 3 and the second sensor 4 detect the temperature at each position, and the resistance value changes according to the temperature. The first sensor 3 and the second sensor 4 are connected to a signal extraction line L via a wiring on the surface 2H side of the substrate 2 and a through hole 21, and the signal extraction line L is connected to a flow detection mechanism 7 composed of a bridge circuit. Is connected to Since the resistance value of the first sensor 3 and the second sensor 4 changes when the temperature changes, the flow rate detection mechanism 7 detects the change as a temperature change. In addition, the separation distance of the closest part along the face plate direction in each of the serpentine portions of the first sensor 3 and the second sensor 4 on the surface 2H of the substrate 2 is set to, for example, 5 mm or less. By setting the separation distance in this way, it is possible to increase the sensitivity of the temperature difference detected by the first sensor 3 and the second sensor 4 according to the flow rate change.

  The heater 5 is a heating wire formed of gold plating 51 and platinum plating 52 similarly to the first sensor 3 and the second sensor 4, and has a portion folded in a zigzag manner between the two through holes 21. As shown in FIG. 3, the serpentine portion of the heater 5 is formed to have a larger amplitude than the serpentine portions of the first sensor 3 and the second sensor 4. The heater 5 is connected to a power supply (not shown), and the voltage is controlled so that a state higher than the gas temperature by a predetermined temperature is realized.

  The flow rate detection mechanism 7 uses the temperature of the first sensor 3 and the second sensor 4 when the gas is not flowing as a reference temperature, and sets the temperature obtained by the first sensor 3 and the second sensor 4 when the gas is flowing. And a signal indicating a flow rate corresponding to a temperature difference from the reference temperature to the outside. Although the flow rate detection mechanism 7 of the first embodiment is a flow rate measurement method based on a temperature difference, for example, the temperature control is performed so that the temperatures of the first sensor 3 and the second sensor 4 are kept constant. The flow rate may be detected based on changes in power consumption or applied voltage.

  Next, the configuration on the back surface 2T side of the substrate 2 will be described in detail.

  As shown in FIG. 4, a honeycomb structure 6 having a plurality of holes 62 defined by partition walls 61 is formed on the back surface 2T of the substrate 2. As shown in FIG. 3, the honeycomb structure 6 is formed on the back side of at least the zigzag portion of the first sensor 3, the second sensor 4, and the heater 5. In the first embodiment, the holes 62 are also arranged on the back side of the platinum plated portion connecting the serpentine portion and the gold plated portion. Assuming that the diameter of the substrate 2 is R, the honeycomb structure 6 is included in a region within an imaginary circle having a radius of 0.35R from the center of the substrate 2, and the outer periphery where the through hole 21 is formed in the substrate 2 The hole 62 of the honeycomb structure 6 is not formed in the portion.

  Each of the plurality of holes 62 has a regular hexagonal column shape extending in the thickness direction from the back surface 2T side to the front surface 2H side of the substrate 2, and is configured to be the densest as a planar filling. The depths of the holes 62 are set to the same depth, so that a predetermined thickness remains on the surface 2H side. That is, each hole 62 forming the honeycomb structure 6 is open at the back surface 2T side of the substrate 2 and has a closed bottom at the front surface 2H side. The partition wall 61 has the same thickness in any part, and the interval between the holes 62 filled in a plane is constant. Further, the honeycomb structure 6 has a predetermined thin plate portion thinner than the thickness of the substrate in the outer peripheral portion of the substrate 2, and the partition wall 61 extends from the predetermined thin plate portion in the thickness direction of the substrate 2 to a predetermined thickness. I can paraphrase it. In addition, each hole 62 is arranged so as to share each wall 61 forming a polygonal side. In the honeycomb structure 6, it is preferable that the area of each hole 62 having the bottomed portion is larger than the area of the partition 61.

  Such a honeycomb structure 6 can be formed, for example, by etching the substrate 2. In other words, each structure in the substrate 2 of the thermal type flow sensor 100 of the first embodiment is formed by MEMS technology.

  According to the thermal flow sensor 100 of the first embodiment configured as described above, the first sensor 3 and the second sensor 4 are formed by metal plating on the surface 2H of the substrate 2 formed of quartz. For example, there is no need to form a resin layer in order to maintain insulation between each sensor and the thin tube as in the case of the capillary type thermal flow sensor 100. Further, since the substrate 2 is formed of quartz, high heat resistance can be realized. Therefore, according to the thermal type flow sensor 100 of the first embodiment, even when exposed to a high-temperature gas such as 300 ° C., the insulation is not broken and the measurement becomes impossible, and the flow rate can be measured.

  Further, since the honeycomb structure 6 is formed on the back surface 2T side of the substrate 2, the heat capacity of the substrate 2 can be reduced. For this reason, even if the substrate 2 is formed of a material having a large heat capacity such as quartz, the temperature change at the surface 2H of the substrate 2 caused by the change in the flow rate can be quickened. Therefore, the response speed to the flow rate can be increased while realizing the heat resistance to the gas.

  Further, instead of simply forming a concave portion on the back surface 2T side of the substrate 2 to reduce the heat capacity, the partition wall 61 that defines each hole 62 is formed, so that mechanical strength can be maintained. For this reason, even if the gas flowing through the flow path C has a high temperature and a high pressure, it is possible to prevent the gas from leaking from the flow path C to the outside due to, for example, cracking of the substrate 2.

  In addition, in the honeycomb structure 6, since each hole 62 is opened on the back surface 2T side of the substrate 2 and the surface 2H of the substrate 2 serving as a gas contact surface is flat, it is necessary to prevent the surface 2H of the substrate 2 from disturbing the gas flow. Can be suppressed. For this reason, the measurement accuracy of the flow rate can be improved.

  Next, a thermal flow sensor 100 according to a second embodiment of the present invention will be described with reference to FIG. The members corresponding to the members described in the first embodiment are denoted by the same reference numerals.

  The thermal flow sensor 100 according to the second embodiment shown in FIG. 5 is different from the thermal flow sensor 100 according to the first embodiment shown in FIG. 2 in that each structure formed on the substrate 2 has a front surface 2H and a back surface 2T. It is configured to be the reverse of That is, in the second embodiment, each hole 62 of the honeycomb structure 6 is opened on the front surface 2H which is the gas contact surface of the substrate 2, and the first sensor 3, the second sensor 4, the heater 5 are formed.

  With the thermal flow sensor 100 according to the second embodiment configured as described above, the honeycomb structure 6 is formed on the surface 2H of the substrate 2, and the heat capacity of the substrate 2 can be reduced. Even if the first sensor 3 and the second sensor 4 are provided on the back surface 2T, a temperature change according to the flow rate can be detected. Accordingly, a flow rate can be measured by detecting a temperature change due to the flow of the fluid on the back surface 2T of the substrate 2.

  Next, a thermal flow sensor 100 according to a third embodiment of the present invention will be described with reference to FIG. The members corresponding to the members described in the first embodiment are denoted by the same reference numerals.

  As shown in FIG. 6, in the thermal flow sensor 100 according to the second embodiment, the portion where the honeycomb structure 6 is formed is only near the first sensor 3 and the second sensor 4, and the honeycomb structure is near the heater 5. 6 is not formed.

  Even in the third embodiment, the effect of reducing the heat capacity of the substrate 2 can be obtained, and the response speed as the flow sensor can be improved as compared with the case where the honeycomb structure 6 is not formed.

  Next, a thermal flow sensor 100 according to a fourth embodiment of the present invention will be described with reference to FIG. The members corresponding to the members described in the first embodiment are denoted by the same reference numerals.

  The substrate 2 according to the first embodiment has a plurality of holes 62 directly formed on the back surface 2T of one substrate 2. However, the substrate 2 according to the third embodiment is different from FIGS. 7A and 7B. As shown in FIG. 1, the main body 22 is formed by penetrating a plurality of holes 62 in the thickness direction, and the lid 23 closing one surface of the main body 22. The lid 23 is adhered to, joined to, or the like with respect to the main body 22 so that airtightness is maintained.

  With such a thermal flow sensor 100 of the fourth embodiment, the honeycomb structure 6 can be formed by penetrating the hole 62 when forming the honeycomb structure 6, and then the lid 23 is attached to the main body 22. The surface 2H can be formed. Therefore, it is easy to accurately form the depth of each hole 62 of the honeycomb structure 6 and the thickness dimension of the surface 2H of the substrate 2.

  Next, a thermal flow sensor 100 according to a fifth embodiment of the present invention will be described with reference to FIG. The members corresponding to the members described in the first embodiment are denoted by the same reference numerals.

  In the first embodiment, each hole 62 of the honeycomb structure 6 is configured to open to the back surface 2T of the substrate 2 and to close the front surface 2H. However, in the fourth embodiment, each hole 62 of the honeycomb structure 6 is 2 is formed on the front surface 2H, and the back surface 2T is formed as a closed bottomed hole.

  Further, the first sensor 3, the second sensor 4, and the heater 5 are formed by plating the end face of the partition wall 61 of the honeycomb structure 6 with metal.

  Even in such a thermal type flow sensor 100 of the fifth embodiment, the heat capacity of the substrate 2 can be reduced, and the response speed to a change in the flow rate can be improved.

  Other embodiments will be described.

  The material of the substrate is not limited to quartz, and may be made of, for example, ceramics such as zirconia.

  The shape of each hole constituting the honeycomb structure is not limited to a regular hexagon. For example, the cross section of each hole may be a polygon such as a square or a triangle, a circle, an ellipse, or the like. In addition, the honeycomb structure in the present specification may be any structure in which a plurality of holes having the same cross-sectional shape are arranged at equal intervals in a plane, and may not satisfy the condition of close-packed plane filling.

  It is sufficient that at least the first sensor and the second sensor are formed on the surface of the substrate, and the heater may be omitted.

  In the third embodiment, the lid is attached to only one surface of the main body. However, a lid may be provided on both surfaces of the main body to form a sandwich structure. By doing so, the mechanical strength can be further increased. Further, the back surface of the substrate may be formed by a lid by combining the third embodiment and the fourth embodiment.

  The thermal type flow sensor according to the present invention is not limited to measuring the flow rate of a high temperature fluid, but may be used for measuring the flow rate at a normal environmental temperature.

  In addition, some or all of the various embodiments may be combined or modified without departing from the spirit of the present invention.

100: Thermal flow sensor 1 ... Flange 2: Substrate 21: Through hole 22: Main body 23: Lid 3: First sensor 4: Second sensor 5 Heater 6 Honeycomb structure 61 Partition wall 62 Hole 7 Flow rate detection mechanism

Claims (8)

A substrate attached so that the surface faces the flow path through which the fluid flows,
A first sensor formed on the front surface or the back surface of the substrate,
A second sensor formed on the front surface or the back surface of the substrate, and disposed downstream of the first sensor;
A honeycomb structure including a plurality of holes extending in the thickness direction of the substrate and defined by partition walls in the substrate.   The thermal flow sensor according to claim 1, wherein the substrate is formed of quartz glass or ceramic. The first sensor and the second sensor are formed on a surface of the substrate,
The thermal flow sensor according to claim 1, wherein the plurality of holes are bottomed holes that are opened on the back surface side of the substrate and the front surface side of the substrate is closed.   The thermal type flow sensor according to any one of claims 1 to 3, further comprising a heater formed on a front surface or a rear surface of the substrate and disposed between the first sensor and the second sensor. The first sensor, the second sensor, and the heater are formed on a surface of the substrate,
The thermal flow sensor according to claim 4, wherein the plurality of holes are formed on the back side of the first sensor, the second sensor, and the heater.   The thermal flow sensor according to any one of claims 1 to 5, wherein a cross-sectional shape of the hole is a regular hexagon.   The thermal flow sensor according to any one of claims 1 to 6, wherein a separation distance between the first sensor and the second sensor in a direction along the surface is 5 mm or less. The substrate has a substantially disk shape with a diameter R,
The thermal flow sensor according to any one of claims 1 to 7, wherein the honeycomb structure is formed in a region within a virtual circle having a radius of 0.35R or less from the center of the substrate.